1. Field of Invention
This invention generally relates to the fields of military vehicles and topographic engineering.
2. Prior Art
Military defilade is where a person or a vehicle is covered from enemy fire and concealed from observation by a physical feature such as a hilltop. Historically the ability for one side in a skirmish to fire from behind a strong wall upon an enemy who is exposed upon an open field has proven a major, sometimes pivotal, advantage for the former.
The current scourge of counter insurgency operations is the roadside bomb, frequently an improvised explosive device, or IED, constructed of a package of 155 mm howitzer shells or an anti-armor shaped charge. Triggered by remote control, they inspire fear and have been very successful in impeding commerce and communications in Iraq and Afghanistan. An ideal response would be to be able to shelter vehicles behind a moving hill top or stone wall which would move in formation with our trucks seemingly on its own, ready to block the shots that otherwise would hit one of our manned vehicles.
There is no system with these capabilities or a similar sacrificial mission. Tanks and APCs can be used in blocking positions, but such a usage is exceptional. Available defensive armor and add-on protective systems do not fully meet the Requirements. Nonetheless, without an illuminating, seminal event from outside the defense community, it is unlikely that such a system will be envisioned and developed. Unmanned ground vehicles, or UGVs, are being widely developed but only for active roles too dangerous for people. Such roles include shooting weapons, searching for mines, and performing chemical warfare or radiation sampling. Active roles which eliminate dangers to humans win developmental funding; it is hard to win money for simply being in the right place. Furthermore, since the unit price could be less than $100,000, industry will not speculatively develop such a product. The delay in deploying unmanned aerial vehicles after the Israelis used them so well in the Bekaa Valley is instructive in that regard.
Two references that will be cited later on are (1) “An Overview of the Shaped Charge Concept,” William Walters, USMA, 11th AUTS, date unknown and (2) Tactical Missile Warheads; edited by Dr. Joseph Carleone; American Institute of Astronautics and Aeronautics; © 1993. Citations will use the acronym TMW. 
Requirements: Vehicles to be Protected
The requirement is to protect light armored vehicles and utility trucks and the people within them. The degree of protection sought is occupant survival without permanent injuries. The models are the M109 High Mobility Multi-Purpose Wheeled Vehicle, or HMMWV, and the Stryker armored vehicle. The HMMWV is approximately 15.8 feet long and 6.2 feet high, and it has a ground clearance of 1.5 feet. The flat vertical area from the bottom of the cab and along the longitudinal axis to be screened is estimated to be 5 feet high and 7 feet long. Stryker is an eight wheeled vehicle approximately 10.3 feet high and 24 feet long. The flat vertical area along the longitudinal axis to be screened is estimated to be 7 feet high and 18 feet long. The area to be protected in the Stryker is 3.6 as large an area as that for the HMMWV. Given that one square foot of armor steel which is one inch thick weighs approximately 41 pounds, a single plate to protect each would weigh 5,200 pounds for the armored vehicle and 1,435 pounds for the utility truck. For greater plate thickness the weight goes up approximately proportionately.
Requirements: Weapons to be Defeated
There are five conventional kill mechanisms to be addressed: bullets and kinetic energy projectiles; fragments of warheads; blast; fire; and all the variants of shaped charge warheads. All these weapons need a direct path to the target for full effectiveness although blast and flames may be able to partially envelop the obstacle.
Kinetic energy weapons are solid projectiles traveling at extremely high speed. They are usually small darts of very dense, rigid material with fineness ratios on the order of 9 to 1. They are a very efficient way to transfer a very large amount of energy to a very small spot on the target. Depleted uranium, about 2.5 times as dense as steel rolled homogeneous armor, or steel RHA, is popular for KE penetrators. The most powerful KE projectiles are fired from the barrels of main battle tanks. The 10 pound penetrator of the 120 mm armor penetrating fin stabilized discarding sabot with tracer (APFSDS-T) is reported to travel at 1.7 km/sec. The one-half pound 30 mm Bushmaster APFSDS-T penetrator and the 1.5 pound 30 mm Bushmaster armor piercing incendiary penetrator are reported to travel at 1.4 km/sec and 1 km/sec, respectively. Fire weapons include flame throwers, Molotov cocktails, and napalm aerial bombs. There are three variants of shaped charges. Each has a hollow space at the front which is enclosed on the sides and back by a metal liner, usually copper. Enveloping the liner from the back end is the main explosive charge. The primary difference between the three being the shape of their liners, they are called the acutely conical liner configuration, the hemispherical liner configuration, and the explosively formed projectile, or EFP. EFP also means explosively forged penetrator.
FIGS. 1a, 1b, and 1c depict the three shaped charge warheads and their liners in that order. In all three the force of the explosion of the main charge fills the liner with an extraordinary amount of energy. This energy causes the liner to collapse inward toward a focal point where it creates a kill mechanism shaped according to how wide or how narrow was the separation of the sides of the liner. Acutely conical liners have included angles of 42 to 60 degrees. Upon the detonation the liner forms two products: a incompressible, fluid stream of metal and a shapeless mass. The stream is called the jet. It is about ¼ inch in diameter, encompasses about 15% of the original liner mass, and travels forward at speeds between 10 km/sec at the tip and 2 km/sec at the tail. (Carleone, TMW, p. 66, and Chi, TMW, p. 465) The shapeless mass, called the slug, encompasses the other 85% of the liner and travels at 1 km/sec. (Williams, p. 2) EFPs, on the other hand, form only one product. The liner angle in an EFP is wide enough that the jet and the slug do not separate but instead form a dart containing virtually all the mass of the liner and travelling at 1.5-3 km/sec. Shaped charges kill primarily by kinetic energy transfer in the products. An acutely conical liner's jet exerts a pressure of millions of pounds per square inch at the tip. When it hits armor, it hydrodynamically erodes its way forward. The shock wave preceding it tears the inside surface of the armor off and shotguns it through the crew compartment as spall. The main kill mechanism is for the jet to emerge inside the armor with enough kinetic energy left to detonate the target's fuel or ammunition. Of the three shaped charges this variant has by far the greatest very hard armor penetration capability. Against such targets an acutely conical design needs to be detonated within about ten times its charge diameter, or CD, for full effectiveness, which is typically five feet or closer. Due to the mechanics of jet formation, about five CDs of standoff is optimal. Against thin armor a greater engagement range is acceptable. For an EFP the kill mechanism is the hypersonic dart. It has much less penetration capability against the hardest, thickest armor, but it can be used against thinner armor from over 150 meters away. Warheads with hemispherical liners are between the other two in liner angles and performance.
The full list of specific weapons that employ these mechanisms encompasses virtually every weapon on the battlefield.                Machine guns        Cannons, both automatic and non-automatic        Rocket-propelled grenades (RPG)        Anti-tank missiles and rockets including recoilless rifle and bazooka projectiles        Bunker buster missiles and rockets        Mortar and artillery rounds        Aerial bombs of all types        Claymore mines and similar blast-fragmentation infantry pyrotechnic devices        Flame throwers and Molotov cocktails        Improvised explosive devices (IED)        
Rocket propelled grenades, anti-tank missiles and rockets, and bunker buster missiles and rockets range from about 60 mm up to about 105 mm in diameter. They generally travel at about 300 msec. Compared to automatic cannon projectiles, they are two to five times as large in diameter and travel at ⅕ to ⅓ the speed. Automatic cannons fire at rates from about 100 rounds per minute to over 1,000 rounds per minute, depending on the specific cannon installation.
As identified earlier, the IED may be the most important of the collection. They have established themselves as powerful psychological weapons, simultaneously iconic for the special hazards of modern counter-insurgency and a dramatic new symbol of the malefactors' destructive power. The extent of the threat from an IED depends on the specific vehicle, its equipment, the specific configuration of the weapon, and the engagement details. Many of the early IEDs in Iraq were stolen 155 mm artillery shells bound together, hidden adjacent to roadways, and detonated when vehicles of interest passed alongside. Even a single six inch shell has a terrible capability; the blast intensity and the density and penetration of fragmentation from a packet is extraordinary.
The weapons to be countered include all current and prior configurations of all the weapons cited and also all their future, improved versions, including those designed specifically to defeat protective armor systems. For defeating protective systems three weapons types are of interest: warheads detonated prior to the target, weapons with included decoys, and dispenser munitions.
Two general approaches used to detonate weapons prior to the target are proximity sensing and time fusing. Both approaches initiate the warhead at a stand-off because it allows a more powerful detonation, creates a more lethal pattern of fragments, or both. As noted, anti-tank shaped charge warheads have a much higher penetration capability when detonated at about five CD from the target instead of on contact. Proximity-fused anti-aircraft projectiles, a standard for U.S. Navy guns since World War II, use proximity fusing for optimal fragment dispersal.
Proximity sensing can be done mechanically, by radio signals, magnetically, and electro-optically. A very widely fielded mechanical proximity sensor is the extensible probe used by the Improved TOW, TOW 2, and TOW 2A missiles. The sensor is a short pole of different specific designs mounted within the missile nose until after launch. After launch it is extended forward and held ahead of the nose. A hard contact by the probe establishes that the missile has reached the desired detonation point and triggers the warhead fuse. Radio frequency sensing is the method for the Navy Mark 53 anti-aircraft fuse. Naval mines frequently use magnetic fusing. Preset time fuses achieve the same results when the distance to the target can be determined and then the time to an optimum detonation calculated and set into the fuse before firing.
Proximity fusing and time fusing from known ranges inject new challenges into the design of on-vehicle defense systems. Shoot-down systems that intercept incoming weapons “in extremis,” meaning immediately before impact, are seriously degraded by any method of standoff fusing. Even a successful hit by the defensive system upon a mechanical proximity fuse may not prevent successful initiation of the warhead anyway. Moreover, non-mechanical proximity fuses and preset time fuses may initiate the warhead of the inbound, attacking missile even before any part of that weapon physically enters the defending system's intercept zone.
Decoys can be used to create time gaps in shoot-down systems. In the new Russian RPG-30 the decoy is a precursor munition that precedes the real munition. It is intended to trigger the vehicle defense system into firing at it. The real weapon follows far enough back to survive the counter fire but closely enough that a new interceptor cannot be launched in time. The company that builds the RPG-30 markets it based on this feature. Of course, the use of decoys is not at all a new tactic; using precursor decoys in advanced RPGs is just a new application.
Dispenser munitions work like a transport bus. After firing or release they travel toward the target and, at some point en route, disgorge separate, smaller kill vehicles, which may be explosive munitions or kinetic energy darts. An example is the fleschette warhead. It transports darts to a preset distance and then releases them to spread to an optimal density before impact. Darts are of different sizes, and heavy darts are massively destructive against light armor. Dispenser weapons challenge the shoot-down active protection systems because the latter must either kill the dispenser prior to release of its cargo, or it must kill all the separate kill vehicles.
Existing Defenses and Their Constraints
There are no unmanned, guided, self-propelled vehicles with a dedicated mission of providing passive protection by being a physical barrier against weapons. At present there are only point defenses on the targets themselves. Against many of the weapons previously cited these point defense systems have no capability.
Tanks and APC's can be utilized as tactical barriers, and it is not uncommon to see such being done in places where maximum security is in effect. During a popular uprising, for example, one highly visible demonstrator of the government's control is to park a couple of tanks in major intersections or to ring the palace with tanks and APC's. These vehicles, however, are highly suboptimal choices for such screening on a wide battlefield or even for wide use in an urban area. Tanks are relatively few in number, and their unique characteristics are largely wasted in blocking positions except of the most important nature. They have extremely high consumption rates for fuel; they require a lot of maintenance; and their sheer size limits their ability to move in urban areas. Further, in urban areas their mere passage tends to do a lot of damage. APC's, on the other hand, have these problems to a much lower degree. Their armor, though, is so thin that many of them cannot effectively shield against all the weapons needed to be defeated. Some of these weapons can shoot right through an APC and still kill the target on the other side. Further the replacement price for both tanks and APC's is too high to allow them to be used freely as sacrificial barriers.
The point defenses to defeat the threats identified include integrated forms of armor and a variety of defensive mechanisms to reduce the attackers' penetration capabilities without adding as much weight as solid metal armor. In very heavy vehicles armor mass has traditionally been provided with steel RHA. In lighter armored vehicles sometimes aluminum armor is used. Despite their massiveness neither of these defenses is sufficient in itself. The closest thing to impenetrable armor is depleted uranium, or DU, armor, which proved itself virtually invulnerable in the Gulf Wars. The problems with providing more defensive capabilities by adding more metal armor include the obvious, negative impact on expense, mobility, fuel consumption, and vehicle maintenance and durability. The most effective option to date, attachable kits of depleted uranium, suffers all these detriments to elevated degrees plus it has unique and severe environmental and political issues.
The less massive approaches include layered armor, explosive reactive armor (ERA), and several externally mounted devices. Layered armor, also called Chobham armor and composite armor, relies on a combination of shock absorption by ceramic plates and, for fluid metal streams, refraction in non-orthogonal layers of different materials. In an ERA system a number of boxes of explosives are mounted on the vehicle exterior. They feature heavy top and bottom plates. When the attacking weapon strikes the ERA box it detonates the explosive which in turn flings the heavy top and bottom plates outward. The penetrator may be impacted by either or both of these interceptors, in which event it may be partially de-energized and partially deflected. There are also some disruptive turbulence effects that linger from the explosion of the box itself. The other devices include a variety of designs to dissipate the energy or otherwise reduce the penetrating power of the kill mechanism. This includes spall liners, which are curtains of fragment resistant fibers emplaced against the inside walls of a target. They prevent the spall created by a strike from being able to spread out unchecked into the compartment. Some composite materials have an increased ability to withstand the metal stream due to their compressibility.
ERA poses a severe threat itself to damage the vehicle on which it rides, especially if there is sympathetic detonation between multiple explosive boxes. It inherently endangers any friendly troops and vehicles nearby, and there are other issues as well.
There are active vehicle defensive systems that are designed to prevent or degrade an attack by intercepting the missile or RPG inbound before it can impact. They are sometimes called hard kill systems. They shoot down the inbound weapon. They fall into two categories, the fly out systems and the “in extremis” systems. Fly out systems launch interceptors to destroy the inbound weapon at a safe distance. Examples of this are the Russian Drozd and Arena systems and the Israeli Trophy system. “In extremis” systems are last moment systems operating right at the edge of destruction. They destroy the inbound weapon within a few inches of an impact. An example of this is the self-titled Iron Curtain system. It detects and tracks inbound weapons by radar and then employs the kill mechanism just before impact. The kill process is to fire an interceptor projectile from one of an array of single shot gun barrels mounted vertically around the roof line of the defended vehicle and pointing down along the vehicle's side.
There are U.S. patents for active protection systems: U.S. Pat. No. 7,202,809 Schade et al is a fly out system, and U.S. Pat. No. 7,954,411 Odhner et al is an “in extremis” system.
There are non-pyrotechnic active protection systems that interfere with an attacking missile's guidance. Called soft kill systems, one example is the Russian Shtora, which combines sensors, an electro-optical jammer, and smoke grenade launchers.
All of these systems are unable to deal with a large portion of the spectrum of threats presented earlier. No fielded APS offers assured protection against a single penetrator fired from a main tank gun; streaming high speed projectiles from direct fire heavy machine guns or automatic cannons; blast; fragmentation; flame weapons of any type; or the hypersonic, fluid, metal streams or liner residue from any of the three shaped charge weapons once the warheads have been detonated. Since they cannot defend against blast and fragments or against hemispherical and EFP shaped charges, none of the fielded shoot down systems has defensive capability against IEDs.
Furthermore, counter measures are being actively pursued to reduce the effectiveness that does exist. A shoot down defense system has to successfully do at least six separate difficult tasks including detect the launch; track the missile or RPG; compute the trajectory; select a defensive weapon to fire; bring it online; and launch it at exactly the right time. Additionally for blast-fragmentation warheads the warhead must be triggered at exactly the right time. These steps have to be done within a specific time line called the reaction time or cycle time. Furthermore the steps all have to be repeated within a certain time for successive shots at different targets or for another shot at the first target. The delay is preparing for successive engagements is the system recycle time.
Every one of these steps constitutes a single point of catastrophic failure. Each task has a discrete probability of failure, and a failure to perform in any of these tasks flawlessly and within the time constraints has a high probability of being fatal. In fact the recycle rate between engagements is the characteristic weakness that the Russian RPG-30 advanced RPG has been designed to exploit: the kill weapon will be too close behind the decoy to allow the defense a second shot.
Furthermore, even if everything works properly the pyrotechnical or KE kill mechanisms of the defense system itself may decimate friendly troops or innocents nearby. Additionally there are severe regulatory controls. All pyrotechnical military systems are wrapped in extraordinary controls on the handling, export, and re-import of original equipment, spare parts, training, and maintenance materials. Everything connected with all their subsystems and accessories are subject to regulations from the State Department; the Bureau of Alcohol, Tobacco, and Firearms; and potentially others.
In U.S. Pat. No. 5,576,508 (1996) Korpi describes a system that transports armor plates and also provides a mechanical apparatus to deploy them prior to entering the engagement. Specifically the stored armor plates are rolled outward away from the vehicle body on carriers at the time of tactical operations. This allows for better overall mobility while still allowing the emplacement of armor at a large number of charge diameters from the target for the purpose of causing suboptimal detonation of shaped charge warheads. The problem with this is that the mass and bulkiness of the system will generate issues in tactical reliability and support, especially in adverse terrain and weather. These problems will be exacerbated by trying to build a system for relatively light vehicles with enough mass or enough standoff between the plates and the target to defeat modern weapons.
The Development Process and the State of the Art in the Subsystems
Engineering development follows fairly standard procedures across industries. For this system, a weapon system, the best model is the U.S. Department of Defense system for material development.
Formal configuration management begins with the requirements and proceeds through three formal baselines that succeed each other in time and in the depth of detail encompassed. The process is depicted in FIG. 2. The Functional Baseline is established when the requirements analysis defines the “what,” “when,” “how well,” and the details. It is captured in an approved System Specification, and it is sometimes called the functional architecture. Next developed is the physical architecture, which is the separate configuration items (CI) and support items that will constitute the solution system. They form the second baseline, the Allocated Baseline, and the new specification is actually the collection of Item Specifications for each of the separate CIs. At this point the CI specifications are not detailed enough to support parts procurement and manufacture. Those are developed next to support procurement, fabrication and test. The last of the three baselines is created. It is the Product Baseline, which is captured in the Product Specification, the Process Specification, and the Material Specification to create the product's manufacturing data package or MDP. The integrated logistics support package is developed in parallel to contain all the technical documents, training programs, test equipment, and other items needed to deploy and support the system.
The systems engineering management schedules follow an event-driven format. Named technical reviews and audits include the Alternate Systems Review (ASR), the System Requirements Review (SRR), the Preliminary Design Review (PDR), the Critical Design Review (CDR), the Test Readiness Review (TRR), the Functional Configuration Audit (FCA), and the Physical Configuration Audit (PCA). At the end of every phase a Requirements Review is conducted to update the Requirement if necessary. Milestone Decision Authority Reviews are held at the end of each phase to support one of three recommendations: continue into the next phase, stay in the current phase for more work, or terminate the program. Monthly Program Reviews between the contractor and the Government PM are the norm. Named management plans help ensure that nothing is overlooked. The Systems Engineering Master Plan (SEMP) is produced by the contractor. The Test and Evaluation Master Plan is prepared by the acquiring PMO in conjunction with the Test and Evaluation Command, which is extremely independent by charter and by historic precedent. The Integrated Logistic Support Plans, or ILSP, are multifaceted and all encompassing.
The U.S. Department of Defense, or DoD, uses a five step systems engineering method for all new systems. FIGS. 3 and 4 show the relationships of the first four steps of the DoD systems design process and some of the key tools.                1. Analyze the Requirements        2. Perform functional analysis of the processed Requirements        3. Allocate the functions to like groups        4. Synthesize a system that carries out the functions        5. Verify the system can do what has been projected.        
The Requirements Analysis produces the Operational View, the Functional View, and the Physical View. Block diagrams show what the parts of a system are, what items sit upon or within what other items, and what the interfaces between them are. Interfaces can include physical interfaces and electrical, fluid, signals, thermal, and other flows. Specific tools include Functional Flow Block Diagrams (FFBD) at multiple levels of detail, time line sheets (TLS), and performance budgets such as the weight budget, the thermal budget, and the electrical power budget. Traceability of requirements is enabled by the numbering system. Every time a specific requirement is broken down each of the newly identified sub-requirements is numbered with the same number as the parent except that a decimal and a sequential number are added. Related functions are grouped together into the Requirements Allocation Sheets (RAS).
The RASs are the pivot point. Using the RASs, FFBDs, and TLSs the designers create design documents like schematic block diagrams (SBD or simply schematics), Concept Design Sheets (CDS), and Design Sheets (DS). They build the physical architecture which includes both the devices and their interfaces. The configuration item (CI) numbers are tentatively written on the RASs next to each and every function each CI will perform. Trade studies lead to iterations. Iteration loops include the Requirements Loop and the Design Loop. These are clearly labeled in FIG. 3.
The formal basis for contracting development is the work breakdown structure (WBS). The WBS captures the most basic issues of the triple constraint: what are we here to do, what are the conditions, and to what standards? It depicts the scope of work including all conditions and performance standards in tabular and graphical form. It allows organization of the work as the assembly and integration of lower level assemblies. The item by itself at the top of the WBS is the system as a whole. The very lowest level is where piece parts and structures are assembled and integrated into functional devices. At the second tier the prime item is on a level with all the separate categories of logistics development, program management, and system engineering.
The WBS depicted in FIGS. 5a, 5b, and 5c is the enterprise template for all DoD surface vehicles from U.S. Military Handbook 881A. For a specific system this template would be tailored as necessary to accurately depict the specific solution selected. Completion of the WBS allows the development of the schedule and the budget. FIG. 6 depicts an extremely simplified, nominal master schedule consisting of a milestone chart atop a Gantt chart, both using the same time line. When a given schedule is resourced the cost can be estimated. Scope, schedule, and budget can be traded for each other, but none can be increased or reduced by itself. Once the program is approved and launched it can be managed with a work authorization system that limits the approved charges to open tasks and with the various methods of supervision.
Objects and Advantages
Accordingly, besides alleviating the shortcomings of the prior art, several objects and advantages of the present invention are:                (a) to provide a stout physical barrier on a separate, unmanned, self-propelled, remotely controlled, expendable vehicle for defense against the weapons listed and effective to the specific design limitations;        (b) to not require the involvement of anyone at the engagement site other than the commander who coordinates in real time with the system controllers;        (c) pending specific implementations, to not use pyrotechnics or dangerous materials and to pose little or no threat to anyone near the vehicle nor to the environment;        (d) pending specific implementations and once in position, to be entirely passive and automatic with zero cycle time to full effectiveness.        